1. Field of the Invention
This invention relates to an optical recording medium in which information writing and/or readout is effected using the light, and a method for manufacture thereof. More particularly, it relates to a magneto-optical disc in which information writing and/or readout is effected using the light illuminated from an opposite side of a substrate, and a method for manufacture thereof.
2. Description of the Related Art
Recently, an optical recording medium in which a heat diffusion layer, a dielectric layer or an information recording layer are formed on a substrate and in which the information is written or read out by the light illuminated on the information recording layer, has come in popular use.
In such optical recording medium, researches are underway for raising the recording density in order to record as much information as possible.
In keeping up with the tendency towards the higher recording density for the optical recording medium, attempts have been made to reduce the diameter of the light spot illuminated on the information recording layer for an optical head configured for writing or reading out signals for the optical recording medium.
In particular, there have recently been conducted researches for constituting a flying optical head by having an objective lens mounted on a slider by application of the technique of the flying magnetic head as used in a hard disc device etc. This flying optical head is flown for facing the layered films on the substrate of the optical recording medium to write or read out information signals from the layered film side of the optical recording medium.
By having the flying optical head flown for facing the layered films on the substrate of the optical recording medium to write or read out information signals, it becomes possible to reduce the distance between the objective lens and the information recording layer of the optical recording medium appreciably in comparison with that in case the light from the optical head is illuminated on the information recording layer via the substrate. This renders it possible to increase the numerical aperture (NA) of the objective lens to reduce the size of the light spot formed on the information recording layer.
If the flying type optical head is flown for facing the layered films on the substrate of the optical recording medium to write or read out the information as described above, the light from the optical head is illuminated from the layered film side. Thus, the layering sequence of the layered films on the substrate in this type of the optical recording medium is reversed from that in the optical recording medium of the type in which the light is illuminated via the substrate.
Meanwhile, if, in the optical recording medium in which the layered films on the substrate are formed in the reverse sequence from that in the optical recording medium irradiated with light via the substrate, the respective layers of the layered films are formed under the conditions similar to those of an optical recording medium of the type illuminated by the light via the substrate, the optical recording medium produced suffers from excessive noise and is lowered in the C/N ratio such that optimum recording and/or reproducing characteristics cannot be achieved.